Oscillation generation



June 18, 1944). VAN SLOQTEN 2,205,233

OSCILLATION GENERATION Filed June 25, 1938 INV EN TdR. JA cos K4 N s: 00 TEN M'II'M/ ATTORNEY.

Patented June 18, 1940 t y l I 2,205,233

UNITED STATES OFFICE t r 2,205,233

QSCILLATION-GENERATION I Jacob van Slooten Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application June 25, 1938, Serial No. 215,742. In Germany September 2, 1937 2. Claims. ((1250-36) This invention relates to a retroactivelycoumeasures'reducing the tendency toward over-ospled'thermionic generator'comprising a grid concillation (blocking) to a minimum value so that denser and a leak resistance. the said dis-advantagesdo not'occur. It is a well-known fact that in oscillators of According to the invention, thisobject is this kind a phenomenon occurs which is referred achieved by the arrangement of meanswhich in ,5 to hereinafter as over-oscillation or"blocking the case of an increase of the amplitude of theand which consists in that the oscillations set up oscillations produced bring about an additional by the-oscillator are periodically interrupted; In charge of a condenser included in the grid circuit. practice, this phenomenon often occurs with 0s- In one form of construction, these means comcillators serving for the productionof short waves. prise a diode which is connected inparallel to 10 Thus, for example, in the construction of superthe grid-cathode space of the oscillator valve and heterodyne receiving sets arranged for therecepwhose anode is connected to thegrid. In another tion of wavelengths from 1 5 to 50 meters this form of cons'tr'uotion-of-the oscillator according phenomenon is particularly troublesome in the to the invention, that part of thecathode conlocal oscillator. ductor which is common to the grid and anode '1;

In order to decrease as far as possible the tend-, circuits includes a condenser which is shunted by.

' 'ency of an oscillator comprising a grid condenser achoke" coil. In. a further form of construction,- and a leak resistance to over-oscillate, it hasprethat part of the cathode conductor which is comviously been proposed to use a small grid conmonto the grid and anode circuits includes a con,

denser. It is also well known that the use of a denser which is shunted byaresistance and whosev 29; small leak resistance-renders the oscillator more electrode connected to the cathode is connected stable. l v y 1 to the grid of the oscillator valve via thegrid The use of a small grid condenser and also that leak resistance. v of a small leak resistance entails disadvantages In order that the invention may be clearly 2.3 that render it desirable to use other measures for understood and readily carried into effect, it will 5 stabilizing an oscillator. nowbe described more fully with reference to the The disadvantage of a small grid condenser accompanying drawing,in which: l consists in the latter being of the order of mag- Fig. 1 shows one form of construction of an nitude of the grid-cathode capacity which in oscillator according to the invention whose operseries with the grid condenser isincluded in-the ation will be more clearly understood by refer- 30 grid circuit in parallel with the highfrequency ence to the curves shown in Fig. 2.,

impedance across which the ieed-backvoltage is FigsB, 4 and 5 show other forms of construcapplied to the grid. This has the efiect of only tion of an oscillator according to the invention. partof the retroactively coupling voltage supplied Fig. 1 shows an oscillator which contains a dis 135 to this impedance occurring across the grid and charge tube l comprising a cathode, a grid and: the amplitude of the oscillations set up by the an anode. The frequency-determining circuit oscillator being consequently small. 1 which is constituted by the parallelcombination In the use of a small leak resistancathis reof condenser 2 and an inductance coil ,3 is insistance brings-about a high attenuationof the cluded in the grid circuit and the anode circuit 40 frequency-determining oscillatory circuit. The includes a feed-back coil 4. In addition, 5 and 6 latter disadvantage is particularly prevalent with designate a grid condenser and a leak resistance an oscillator serving as the local oscillator in a respectively which are included in the circuit in superheterodyne receiver which is arranged both well known manner andare proportioned in the for the reception of waves from about 15 to usual manner. I 5 meters and for the reception of at least one band The circuit hitherto described has a tendency 45, of longer waves. Since the impedance of the to over-oscillate, that is, block. In order to exfrequency-determining oscillatory circuit of' an plain the cause of this phenomenon, let usassume oscillator increases on the reception of short a givenposition of equilibrium at which the oswaves being switched over to aband of longer cill'ator setsup oscillations of constant amplitude. 5Q waves, the attenuating effect of the leak resist- In thispositioh of equilibrium, the grid condenser 50 ance on the oscillatory circuit increases. This 5 is charged by-the grid current to a voltage which necessitates switching over of the leak resistance is higher negative than the voltage at which the on the reception of the band of longer waves to a anode current is suppressed in the absence of oshigher value, which renders the set complicated. cillations. The condenser voltage determines the The invention has for its object to provide grid bias of the oscillator valve and thus the point passes through the diode I.

When for some reason or other, for example on account of a small increase of the anode direct voltage, the amplitude of the oscillationsgenerated exceeds the said constant value, the effective mutual conductance ofthe oscillator valve increases, since the anode direct current increases to a higher extent than the amplitude of the oscillations generated. Due to the increasing mutual conductance of the oscillator valve,'the amplitude of the oscillations produced increases to a still higher extent, which in turn results in an increase of the mutual conductance. Thus the above-assumed position of equilibrium becomes unstable and this lack of stability is the cause of the phenomenon of over oscillation.

According to-the invention, in order to suppress the tendency to over-oscillate, the grid-cathode space of the oscillator valve has connected in parallel with it a diode 'I-whose anode is connected to the grid of the tube I;

If the amplitude'of the oscillations produced increases, the condenser 5, due to the presence of the diode I, is charged by the grid current which increases with an increasing amplitude of the oscillations set 'up as well .as by the current that Consequently, in the case ofan increasing amplitude of the oscilla tions produced, the condenser 5 will have occurring across it an additional negative voltage which displaces the workingpoint of the characteristic curve to a point at which the mutual conductance is lower. In the circuit shown in Fig. 1, the effective mutual conductance would therefore increase, in the case of a deviation from the position of equilibriun -by reason of an increase in' the amplitude of the oscillations to be set up. On the other hand, the additionalvoltage (i. e., the negative bias) across the condenser 5 would bring about a decrease of the efiective mutual conductance. Thus, both a c t i o n s counteract each other, which avoids any disturbance in the position of equilibrium of the amplitude of the oscillations set up.

In the form of construction shown in Fig, 3 the diode 1 is arranged within the oscillator valve, since the latter comprises an additional electrode 8 arranged adjacent the control grid and the cathode of the oscillator valve. This supplementary electrode 8 constitutes withthe cathode a diode which increases the current that passes through the grid circuit in the case of an in creasing amplitude of the oscillations set up, said current bringing about an additional charge of the condenser 5,

In the form of construction shown in Fig. 4, that part of the cathode conductor which is common to the grid and the anode circuits includes a condenser 9 shunted by a choke coil I0. The anode direct' current passes through the choke coil which constitutes a short 'circuit for the condenser." In the case of an increase of the amplit'ude'of the oscillations set up, a variation in Fig. 5'. In this circuit,

the mean anode current occurs. Thusthe condenser 9 becomes charged so that a negative voltage occurs across the condenser 9, said voltage being supplied to the grid of the valve I and displacing the working point of the oscillator valve to a point of less steepness.

A circuit inwhich a resistance I I is substituted I for the choke coil required in Fig. 4 is shown in the grid leak 6 is connected to that point of the condenser 9 which is connected to the cathode so that the direct voltage drop which occurs across the resistance II due to the mean anode current is prevented from being supplied to the grid. The voltage which occurs across the condenser 9 in the case of a variation of the mean anode current is, however, supplied via a condenser 5 to the grid of the oscillator valve I.

What is claimed is:

l. A retroactively coupled oscillator comprising an electron discharge device containing a grid, an anode and a cathode, a frequency determining circuit having one terminalconnected to said grid through a grid condenser, a choke coil shunted by I a by pass condenser having one end connected to said cathode and the other end connected to the other terminal of said frequency determining circuit, a leak resistor connected between said grid and said last end of said choke coil, a connection from said anode also to said last end of said choke coil,- said connection being coupled to said frequencydetermining circuit for feeding back energy from said anode, said device considered together with said grid condenser and leak re-' sister functioning to bias said grid in proportion to the strength of oscillations, said Icy-pass condenser being a path of low impedance to energy of the operating frequency and the combination of said choke coil and Icy-pass condenser having high impedance to sudden changes in average current passing therethrough, whereby said combination of choke and by-pass condenser function to impart an additional voltage to said grid which is proportional to the rate of change of the average anode current.

2. A retroactively coupled oscillator comprising an electron discharge device containing a grid, an anode and a cathode, a frequency determining circuit having one terminal connected to said grid through a grid condenser, a choke coil shunted by a by-pass condenser having one end connected to said cathode and the other end connected to the other terminal of said frequency determining circuit, a leak resistor connected be tween said grid and said last 0011, means for feeding back anode to said frequency determining circuit, said denser apply an additional bias to said grid in proportion'to the algebraic value of the rate 01" change of the oscillation amplitude.

JACOB VAN SLOO'IEN. 

